1. Field of the Invention
The field of the invention relates generally to management of distributed DC power sources, and even more particularly to maintaining reliability in distributed DC power sources, such as fuel cells, solar array applications, etc., in the case of component malfunction.
2. Related Arts
Distributed power harvesting system generally comprise several DC power sources, such as, e.g., batteries, fuel sells, solar panels, etc., that are connected together to form a power supply. Batteries with numerous cells or hybrid vehicles with multiple fuel cells are examples of DC power sources whose power is accumulated through a series connection in a distributed power harvesting system. Another example is photovoltaic (PV) cells or solar panel power system. Solar energy is obtained from solar cells that provide a clean alternative source of energy. Solar installations include solar panels that convert the light energy to electric power and electronic power harvesting systems that harvest the electric power from the panels and convert it for domestic use. The electronic system is generally referred to in the art as balance of system (BoS).
Each of the individual DC power sources usually provides low voltage (e.g., batteries normally provide less than 3 volts) and low current. Consequently, DC-DC converters are used together with various series and parallel topologies to convert the DC power provided from the DC power sources into the required voltage and/or current. In some applications, each DC power source is connected to its own DC-DC converter, and the outputs of the converters are coupled in series or parallel topology.
Maintaining reliability in both series and parallel connections is important. Malfunction of one may disturb the operation of the entire installation. For example, in series connections an open circuit malfunction in one converter may stop the flow of current in the entire series connection. On the other hand, in parallel connection a short malfunction in one arm of the circuit would reduce the voltage between the parallel nodes to zero.
FIG. 1 illustrates one possible architecture for distributed power harvesting system. In the system of FIG. 1, each DC power source 101, for example, battery, fuel cell, solar panel etc., is connected to its own associated AC module 109. The AC module 109 may include a DC-to-DC converter 105 and an inverter 114 (when the load requires alternating current). The converter 105 is used for DC to DC conversion of the input voltage—usually as means of maximizing power output from DC source by staying at maximum power point. The inverter 114 is used for inversion of the DC input to an AC output. As such, the power conversion and inversion is distributed within the circuit as opposed to being performed on a centralized collection of the power from the entire circuit. The input of each AC module 109 is connected to one of the panels 101. Each AC module may be used independently and individually. Alternatively, outputs of the AC modules 109 may be connected in parallel to an AC bus 111. The AC bus 111 may be connected to the load, such as, for example, the electric box of a house.
FIG. 2 illustrates another possible architecture for distributed power harvesting system using multiple DC power sources. In the system of FIG. 2, each DC power source 101, e.g., battery, fuel cell, solar panel, etc., is connected to its own associated DC-DC converter 205. As such, the power conversion is distributed within the circuit as opposed to being performed on a centralized collection of the power from the entire circuit. The converters 205 are connected in series to provide a string of serially connected DC converters. The output from the series connection of the converters 205 is provided to the common inverter 104. The converters 205 are DC-to-DC converters and the DC current and voltage are converted to an alternating current at the inverter 104.
In power harvesting from distributed sources, if one of the components in a series-connected group of power sources fails, the circuit is liable to become open and disconnect the current. If one of the components in a parallel-connected group of power sources fails, the circuit is liable to short the current through the entire parallel connection and take the voltage to zero. The reliability of the components is crucial to the success of distributed installations. The cost of parts and labor for maintenance and replacement of parts are burdensome, especially when considering the fact that the components may be located on roofs and other hard-to-get locations. Therefore, there is a need to increase the overall reliability of the components in distributed power harvesting systems.